The use of such a sliding sleeve is well known in constant-mesh gear transmissions of the synchromesh type, e.g. as described in "Principles of Automotive Vehicles", Manual TM9-8000 and TO36A-1-76, published January 1956 by the Department of the Army and the Air Force, pages 234-238. In the system described in that publication, the sleeve is in permanent mesh with a sliding gear splined to a main shaft and is releasably connected therewith for limited joint axial motion by a set of spring-loaded ball checks. The sliding gear and the coaxial gear to be driven thereby are provided with confronting frustoconical clutch surfaces which are separated by a small clearance in a decoupling position but contact each other when the first gear and its sleeve are axially moved toward a coupling position. The second gear is then frictionally entrained and accelerated (or possibly decelerated) until its speed substantially equals that of the first gear. Only then can the teeth of the sleeve enter between the teeth of the second gear, the two sets of teeth being suitably beveled at their confronting ends to facilitate the meshing engagement.
In lieu of a sliding gear it is also possible to use in such a system an axially fixed driving gear together with a so-called synchro ring coaxially interposed between the two gears, the synchro ring rotating with the driving gear but being axially entrainable by the sleeve through ball checks or the like to establish frictional contact between a clutch surface on that ring and a confronting clutch surface on the driven gear. Upon the establishment of such contact, the sleeve is released from the synchro ring and can be axially slid into engagement with the driven gear.
The completion of the shift of the sleeve into a coupling position, however, is not always smooth with either type of system and, when carried out too rapidly, could still give rise to annoying gear clashing.